unreadable HP cartridges
ard at p850ug1.demon.co.uk
Thu Jun 23 13:28:45 CDT 2005
> > Digital information is stored on the tape using a delta distance
> > encoding scheme. The "1" distance is approximately 1.75 times
> > longer than the "0" distance. The magnetic polarity is
> > irrelevant, only the distance is important.
> This is very similar to the Apple II cassette modulation scheme.
> Hmm.. Woz worked for HP at the time...
> If you look at other early cassette tape "standards" they tend
> to be more FSK-like than distance-encoding type. e.b. Kansas
> City Standard.
The other comman standard at about this time -- used by the HP 9830 on
cassette tapes, on the Tekky 4051 on QIC cartrisges and by the HP65/67/41
on magnetic cards was to have 2 tracks. A pulse on one of the tracks is a
'0' bit, a pulse on the other is a '1' bit. Coincident pulses on both
tracks might be used for something like a file marker or a byte marker
(the HP 9830 does the latter).
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